EP0707018B1

EP0707018B1 - Stabilised core resin particles for use in resin compositions and processes for making

Info

Publication number: EP0707018B1
Application number: EP95307012A
Authority: EP
Inventors: Barkev Keoshkerian; Stephan Drappel; Michael K. Georges
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1994-10-03
Filing date: 1995-10-03
Publication date: 1998-12-16
Anticipated expiration: 2015-10-03
Also published as: HK1011698A1; CA2153718A1; US5714993A; CA2153718C; US5545504A; JPH08176216A; DE69506661T2; BR9504256A; EP0707018A1; DE69506661D1

Description

The present invention is generally directed to processes for the preparation of stabilized core resin particles for use in toner compositions and processes for using the toner composition in ink jet printing applications. More specifically, the present invention relates to processes which provide sterically and/or electrostatically stabilized in situ resin compositions and stabilized pigment particles which are suitable for use in electrophotographic imaging and ink jet printing methods.

Conventional free radical polymerization processes that have been used to polymerize unsaturated or olefinic monomers inherently provide broad polydispersity resin products or require that sophisticated processing conditions and materials handling protocols be employed to control, to some extent, the polydispersity properties of the resin products, for example, carefully controlling reactor temperature profiles or monomer addition rates. The resin products prepared from the aforementioned conventional free radical polymerization processes generally require post reaction processing, such as isolation and purification, before the resin product is in a suitable condition for formulating with other components, such as colorants and charging additives, for the purpose of preparing dry or liquid toner particle formulations.

Many known polymerization processes used for the synthesis of narrow polydispersity resins, such as anionic, cationic, and group transfer polymerization processes, are severely limited by the need for anhydrous reaction conditions and monomers which do not contain protic or reactive functional groups, for example, hydroxy (OH) carboxy (CO₂H) and amino (NH). As a consequence, these processes are not readily applicable to the polymerizaton of functionalized monomers since these monomer materials tend to be chemically reactive or hydroscopic whereby any associated water may readily destroy the polymerization initiator component, for example, the hydrolysis or protonation of organolithium reagents that are used in anionic polymerization processes, or in other ways cause the polymerization to fail entirely or to be industrially inefficient.

It is generally accepted that known anionic and cationic polymerization processes used for the preparation of narrow polydispersity resins, diblock and multiblock polymers are not believed possible in aqueous or protic solvent containing polymerization media, or in the presence of aforementioned protonic or reactive functional groups. Control of the polydispersity and blockedness of the resin enables control of toner melt rheology properties such as T_g and hot offset temperature, reference, for example, US-A-5,312,704.

Of the known polymerization processes a preferred way to prepare polymers or copolymers having a narrow molecular weight distribution or polydispersity is by anionic processes. The use and availability of resins having narrow polydispersities in industrial applications is limited because anionic polymerization processes must be performed in the absence of atmospheric oxygen and moisture, require difficult to handle and hazardous initiator reagents, and consequently such polymerization processes are generally limited to small batch reactors. In addition, the monomers and solvents that are used must be of high purity and anhydrous thereby rendering the anionic process more expensive and tedious than alternatives which do not have these requirements. Thus, anionic polymerization processes are difficult, costly and dangerous. It is desirable to have free radical polymerization process that provides narrow molecular weight distribution stabilized resin particles that overcomes the shortcomings and disadvantages of the aforementioned anionic and related polymerization processes.

Similarly, group transfer polymerization (GTP) processes have limitations and disadvantages, such as anhydrous reaction conditions and expensive reagents, which disadvantage GTP processes for large scale industrial applications.

Free radical polymerization processes are generally chemically less sensitive than anionic processes to impurities in the monomers or solvents typically used and are substantially or completely insensitive to water. There has been a long felt need for an economical free radical polymerization process which is suitable for directly preparing narrow polydispersity resins, stabilized resin and toner particles, and stabilized pigment particles by free radical reaction processes.

Copolymers prepared by conventional free radical polymerization processes inherently have broad molecular weight distributions or polydispersities, generally greater than about four. One reason is that most free radical initiators selected have half lives that are relatively long, from several minutes to many hours, and thus the polymeric chains are not all initiated at the same time and which initiators provide growing chains of various lengths at any time during the polymerization process. Another reason is that the propagating chains in a free radical process can react with each other in processes known as coupling and disproportionation, both of which are chain terminating and polydispersity broadening reaction processes. In doing so, chains of varying lengths are terminated at different times during the reaction process which results in resins comprised of polymeric chains which vary widely in length from very small to very large and thus have broad polydispersities. If a free radical polymerization process is to be enabled for producing narrow molecular weight distributions, then all polymer chains must be initiated at about the same time and premature termination by coupling or disproportionation processes must be avoided or eliminated.

Contemporary environmental issues and pollution concerns are prompting greater use of certain biodegradable polymers, among these are water soluble polymers as described by F. Lo, J. Petchonka, J. Hanly, Chem. Eng. Prog., July, 1993, p. 55-58.

Conventional processes for preparing sterically and/or electrostatically stabilized resin or sterically stabilized pigment particles are confounded by the aforementioned problems of anionic and cationic processes which require scrupulously dry solvents and reactants, and monomer compounds without reactive functionality. Other stabilization processes known in the art use oxygenated polymeric compounds, such as polysaccarides, as macromolecular steric stabilizers. These stabilizer compounds are either physi-sorbed or physically embedded into the surface of the resin or toner particles. Covalent attachment of these and other stabilizer compounds to the particle surface has proven to be a difficult and expensive proposition. Oxygenated polymeric steric stabilizer compounds typically render the resulting particles humidity sensitive thereby making the resultant stabilized dry toner particles and developer compositions also humidity sensitive.

The following patents are of interest.

In US-A-5,728,239 there is disclosed a process for producing a coupled polymer by anionically polymerizing monomers.

US-A-4,597,794 discloses an ink-jet recording process in which the ink is prepared by dispersing fine particles of pigment in an aqueous dispersion medium containing polymer having both a hydrophilic and a hydrophobic construction portion.

US-A-4,846,893 discloses a process for producing a surface treated pigment wherein a vinyl polymer layer is formed on the surfaces of the pigment particles.

US-A-4,476,210 discloses a stable colored liquid developer and method for making such wherein an improved optical density resulting from a colored dye being imbibed into a thermoplastic resin core occurs.

US-A-5,281,261 discloses an ink composition comprising an aqueous liquid vehicle and pigment particles having attached to the surfaces thereof a polymerized vinyl aromatic salt.

US-A-4,530,961 discloses an aqueous dispersion of carbon black grafted with hydrophilic monomers such as alkali or ammonium carboxylate bearing polymers.

US-A-4,314,931 discloses a process for substantially eliminating polymerization inhibition in a pigment containing dispersion polymerizaton reaction, which comprises grafting polymer molecules onto the pigment used in the polymerizaton reaction, whereby there results a polymerized product which contains essentially no monomer material.

US-A-4,581,429 discloses a free radical pseudoliving polymerization process which controls the growth of polymer chains to produce short chain or oligomeric homopolymers and copolymers including block and graft copolymers.

US-A-5,059,657 discloses a polymerization process for acrylic and maleimide monomers by contacting the monomers with a diazotate, cyanate or hyponitrite, and N-chlorosuccinimide, N-bromosuccinimide or a diazonium salt. The polymer produced can initiate further polymerization, including use in block copolymer formation.

WO94/11412 describes a free radical polymerization process for the preparation of a thermoplastic resin involving the use of a stable free radical agent.

In free radical polymerization reaction processes of the prior art, various significant problems exist, for example difficulties in predicting or controlling both the polydispersity and modality of the polymers produced. These processes generally produce polymers with high weight average molecular weights (M_w) and low number average molecular weights (M_n) resulting in broad polydispersities or low molecular weight (M_n) and in some instances low conversion. US-A-4,581,429, reference the examples, see especially Examples 34A and 34B, illustrates narrow polydispersities of the example 1.15, however the conversion is low, less than about 22% for example, and this process utilizes a reaction adduct or product of a carbon centered free radical and a stable free radical to initiate polymerization. Further, generally the free radical polymerization processes of the prior art are prone to generating excessive quantities of heat since the polymerization reaction is exothermic. As the viscosity of the reaction medium increases, dissipation of heat becomes more difficult. This is referred to as the Trommsdorff effect as discussed and illustrated in Principles of Polymerization, G.Odian, 2nd Ed., Wiley-Interscience, N.Y., 1981, page 272. This is particularly the situation for reactions with high concentrations of soluble monomer, for example greater than 30 to 50 percent by weight soluble monomer, which are conducted in large scale reactors with limited surface area and limited heat dissipation capacity. Moreover, the exothermic nature of free radical polymerization processes is often a limitation that severely restricts the concentration of reactants or the reactor size upon scale up.

Further, gel body formation in conventional free radical polymerization processes may result in a broad molecular weight distributions and/or difficulties encountered during filtering, drying, dissolving, and manipulating the product resin, particularly for highly concentrated reactions.

Practitioners in the art have long sought an inexpensive, efficient and environmentally efficacious means for preparing stabilized resin and pigment particles, and which stabilized particles are suitable for use in preparing dry and liquid developer compositions and imaging processes.

Thus, there remains a need for polymerization processes for the preparation of narrow polydispersity reactive emulsifier compounds and polymeric resins, and for derivatization processes for preparing stabilized resin and pigment particles by economical and scalable free radical polymerization techniques and which polymers and particles retain many or all of their desirable physical properties, for example, hardness, low gel content, processability, clarity and high gloss durability while avoiding problems such as gel formation, exotherms, volume limited and multi-stage reaction systems, purification and performance properties of the polymer resin products associated with prior art free radical polymerization and particle stabilization methodologies.

It is an object of the present invention to provide such processes, and the resulting toner compositions.

According to one aspect, the invention provides a process for the preparation of stabilized core resin particles comprising: forming a mixture comprised of at least one free radical reactive monomer, a colorant, a stabilizer compound containing a stable free radical reactive group, and a liquid vehicle; and heating the mixture from about 75 to about 200°C to effect polymerization of said monomer. There results stabilized core resin particles containing said colorant, wherein said stabilized core particles are stabilized by said stable free radical reactive stabilizer compounds being bonded directly to the core particles.

In a preferred aspect herein, the monomer is a hydrophobic monomer selected from the group consisting of monovinyl aromatic compounds and derivatives thereof, dienes and derivatives thereof, and acrylates and derivatives thereof.

In another preferred aspect herein, the polymeric stabilizer compound is of the formula (A-B)-SFR is selected from the group consisting of poly(styrenesulfonate-b-styrene)-SFR, poly(acrylic acid-b-styrene)-SFR, and poly(alkyl acrylate-b-styrene)-SFR wherein -SFR is a covalently bonded and thermally labile stable free radical functional group.

In a further preferred aspect, the process further comprises adding to the mixture prior to heating a thermoplastic resin selected from the group consisting of polystyrenes, polyacrylates, polymethacrylates, polydienes, mixtures thereof, and copolymers thereof, and wherein the resin is soluble or dispersible in the monomer component.

According to another aspect, the invention provides a toner composition comprising a liquid carrier vehicle, and marking particles comprised of core resin, a colorant, optional additives, and at least one stable free radical reactive polymeric stabilizer compound. Preferably the polymeric stabilizer compound is substantially chemically bound or covalently attached to the core resin, and wherein a hydrophobic end of the stabilizer compound is substantially embedded in the core resin particles and a hydrophilic end of the stabilizer compound is substantially distal to the particle surface.

The present invention also relates to polymerization processes for preparing stabilized resin particle products that possess narrow molecular weight distributions or polydispersity properties and narrow particle size distributions, and which polymerization processes proceed with high monomer to polymer conversion. In particular, the present invention relates, in embodiments, to polymerization processes which directly yield stabilized resin particles having resin number average molecular weights (M_n) equal to or above 2,000 to 500,000 and having a polydispersity ratio of the weight average molecular weight (M_W) to the number average molecular weight (M_n) of from 1.0 to 2.0, and preferably 1.1 to 1.5. As used herein, the term "stabilized" refers to known electrostatic and/or steric solid-liquid or colloidal dispersion phenomena. The stabilized resin particles and stabilized pigment particles that are formed by in situ monomer polymerization reactions and pigment coupling reactions, respectively, in embodiments, may be used directly in selected liquid based imaging applications without the need for further processing steps, such as isolation, purification and classification. In other embodiments, the present invention provides processes for preparing stabilized pigment particles, which stabilization processes provide an alternative approach to conventional methods for stabilizing typically unstable pigment particle dispersions for use in, for example, aqueous and non-aqueous ink jet ink formulations. The present invention also provides, in embodiments, a pseudoliving polymerization process that enables the direct preparation of narrow polydispersity homopolymeric and copolymeric "reactive emulsifiers" which may be used to prepare stabilized resin particles directly from monomers; and stabilized pigment particles. In embodiments, first formed intermediate polymers, alternatively referred to as stabilizer compounds or reactive emulsifiers, are of the formula ( I - A - B -)-SFR where I is a free radical initiator molecular fragment, A is a polymeric segment and B is a polymeric segment and which segments can be the same or different in composition and physical properties, and SFR represents a covalently bonded and thermally labile latent stable free radical functional group. The intermediate polymers may be optionally isolated and stored indefinitely at ambient temperature or reacted directly, or in situ, with additional monomer or monomers to form stabilized resin or pigment particles. The processes of the present invention can, in embodiments, use known free radical initiators in combination with, for example, an oxygenated stable free radical agent, and a free radical reactive, polymerizable, monomer or monomers to afford stabilized, narrow polydispersity, homo- and copolymeric resin particles. The aforementioned resin particle formation and stabilization processes can optionally incorporate a colorant into the reaction mixture before, during, or after polymerization to provide particle coloration capability. In an alternative embodiment, the aforementioned stabilized pigment particles may be added to the aforementioned stabilized resin particle formation process to provide enhanced pigment dispersion and stability properties to the resulting pigmented resin particles or toner particles. Enhanced pigment dispersion and stability in toner particles in turn imparts desirable image quality characteristics to electrophotographic and liquid ink impressions and transparencies, particularly for color images, for example, high fidelity color reproduction and transparency projection efficiencies.

The present invention provides intermediate product polymers containing a latent, thermally reactive, functional group on at least one end of the polymer molecule which are subsequently used in reactions to prepare resin particles with desired resin architectures, particle size, and colloidal stability properties. The present invention, in embodiments, provides polymerization processes that enable control of resin molecular weight, weight distribution, modality and homogenity of the products.

The present invention is also directed to pseudoliving polymerization processes which permit the economic preparation of narrow polydispersity resins with low, intermediate, or high molecular weights. The low molecular weight resins can be prepared without a chain transfer agent or molecular weight modifier which provides several advantages over conventional chain transfer mediated polymerization processes.

The polymerization processes, thermoplastic resin products, and stabilized resin and pigment particle formulations of the present invention are useful in many applications, for example, specialty applications including toner, liquid immersion development ink resin particles, and ink jet inks and performance additives for electrophotographic and non-electrophotographic imaging processes.

The invention provides polymerization processes for the production of diblock and multiblock resins and thermally labile, free radical reactive, emulsifiers having narrow molecular weight polydispersity properties and with high monomer to polymer conversion.

The invention provides pigment stabilization processes which embody the direct reaction of the aforementioned thermally labile reactive emulsifier or stabilizer compounds with pigment particles, such as carbon black, to provide surface modified and dispersion stabilized pigment particles.

In another aspect of the present invention there is provided, in embodiments, a polymerization process for the preparation of stabilized thermoplastic resins and toner resin particles comprising forming a mixture comprised of at least one free radical reactive monomer, a colorant, a stabilizer compound containing a thermally labile and covalently bound stable free radical reactive group, an optional emulsifier, and an optional polymeric resin wherein the optional resin is soluble or dispersible within the monomer, and a liquid vehicle; and heating the mixture to effect polymerization of the monomer, wherein there results stabilized core resin particles containing the colorant and wherein the stabilized core particles are stabilized by the covalently appended stable free radical and stable free radical reactive stabilizer compound fragments. In embodiments of forming the aforementioned reactive stabilizer compound, it is important that the free radical initiator and stable free radical agent be added as separate components and wherein a reaction therebetween is avoided.

In another aspect of this invention there are provided processes for the preparation of sterically and/or electrostatically stabilized resin particles which stabilized particles can be subsequently thermally destabilized or otherwise surface modified by additional stable free radical mediated chemical reactions, for example, adding additional monomer and heating to provide surface hydrophobicity altered particles.

In another aspect of the present invention there is provided a polymerization reaction system which affords ink jettable toner particles, that is a thermal ink jet ink composition which is thermally stable prior to jetting and may be subsequently readily jetted by known means and then fixed to a receiver member by thermal, irradiation, or pressure means at 25°C to 150°C.

The invention provides a polymerization reaction system which may be conducted in the presence of conventional free radical polymerization inhibiting pigments such as carbon black.

The invention enables the preparation of water soluble or water dispersible thermoplastic resin particles by single pot processes employing suitable monomer or monomers, free radical initiator, optional minimal amounts of an emulsifier or surfactant which may provide rate enhancement or simplify isolation, but avoids emulsification or phase separation during the polymerization, and a stable free radical agent.

In yet another aspect of the present invention there are provided an imaging method and ink jet compositions for producing fused images which possess desirable latency, recoverability, kogation, mid frequency line edge noise (MFLEN) or edge raggedness, high resolution of from 120 to 240 spots per cm colorfastness, water fastness, reduced spattering, and dispersion stability.

The invention enables the preparation of resins and stabilized resin particles using polymerization processes wherein the molecular weight of the growing polymer or copolymer chains increase over the entire time period of the polymerization reaction and wherein the percent conversion or degree of polymerization of monomer to polymer with respect to time or number average molecular weight is approximately linear, that is, polymerization processes which occur without the aforementioned Trommsdorff effect.

In other embodiments the polymerization processes of the present invention can be used to prepare reactive emulsifiers or stabilizer compounds that comprise diblock copolymers or multi-block polymers with narrow polydispersity properties wherein at least one of the blocks is water soluble and subsequently added blocks or segments may be partially or entirely water insoluble and wherein the polymer contains a covalently bonded and thermally labile stable free radical functional group thereby providing a means for preparing surfactant materials with well defined polydispersity and hydrophobe-lipophobe balance (HLB) properties and containing a latent or masked free radical terminal functional group which is capable of further free radical addition polymerization reactions or coupling reactions.

The processes of the present invention, in embodiments, comprise a means for the direct preparation of stabilized dry and liquid toner particle compositions and stabilized pigment particles which are suitable for use in electrophotographic and ink jet imaging and printing applications, including color processes. The stabilizer molecules or reactive emulsifiers and the polymer resins produced by processes of the present invention, in embodiments, are essentially monomodal, that is the molecular weight distribution is narrow and indicative of a Poisson character and without substantial shoulders or side bands.

In embodiments, by repeating the heating step, comprising the combined initiation and polymerization step, there is provided a means for obtaining monomodal mixtures of polymer resins that are compositionally the same resin type with characteristics of both narrow polydispersity and known or selectable modality greater than 1.

Moreover, in embodiments, the process of the present invention provides a means for conducting polymerization processes on multikilogram or larger scales. The aforementioned embodiments may be accomplished in a one or single pot reactor environment. In embodiments, polymeric chain growth proceeds by a pseudoliving mechanism and can provide resins of desired weight average molecular weights from very low to very high, for example, less than 2,000 to in excess of 500,000, for example, up to about 700,000, while maintaining reasonably narrow molecular weight distributions or polydispersities.

Further, in embodiments, the processes of the present invention provide an efficient means for preparing high molecular weight, for example, in excess of 250,000 to 500,000 weight average molecular weight polymeric resins, comprising preparing and isolating a stable free radical terminated reactive emulsifier compound with a weight average molecular weight of 10,000 to 50,000 and preferably 30,000 in accordance with the aforementioned stable free radical polymerization processes and thereafter reacting the isolated reactive emulsifier compound with appropriate amounts of additional monomer. The resulting stable free radical terminated polymer possesses substantially higher molecular weight properties; is substantially purier; and is obtained in substantially less time, that is shorter reaction times for a given temperature range, than the corresponding de novo polymerization processes. A concommitant advantage of the aforementioned two stage reaction process is the ability to conduct particle formation and stabilization processes of the present invention at higher solids levels or concentrations, for example, at 10 to 50 weight percent solids and above.

In embodiments, the block and multiblock copolymers of the aforementioned stabilizer compounds or reactive emulsifier can be prepared by the aforementioned stable free radical moderated polymerization processes wherein each block formed is well defined in length by the sequentially added and reacted monomer and wherein each additional block that is formed also possesses a narrow molecular weight distribution.

Processes for the preparation of toner compositions in accordance with the invention will now be described, by way of example, with reference to the accompanying drawings, in which:-

Figure 1 illustrates an exemplary scheme for preparing stabilized resin particles of the present invention using reactions of a reactive emulsifier and a preformed resin particle having free radical reactive sites on or at the resin particle surface;

Figure 2 illustrates an exemplary scheme for preparing stabilized resin colored particles of the present invention; and

Figure 3 illustrates an exemplary scheme for preparing stabilized pigment and resin particles of the present invention.

The present invention provides polymerization processes for preparing stabilized polymeric resin particles with well defined molecular weight properties and narrow polydispersities. The present invention provides processes which are also applicable to the preparation of stabilized pigment particles. The processes can be performed as batch, semi-continuous or continuous processes. The processes provide for from 5 to 99 percent by weight of the reaction mixture to be monomer or monomer mixtures and the processes are conducted at from 100°C to 180°C and preferably from 120°C to 140°C. The processes produce polymer products and stabilized particles having low, intermediate, or high molecular weights; and narrow resin and stabilizer compound polydispersities.

In embodiments, the present invention overcomes the problems and disadvantages of the prior art polymerization processes by forming narrow, for example, 1.1 to 1.8, preferably 1.1 to 1.5, and most preferably 1.1 to 1.3, polydispersity polymeric resins by means of, for example, a single pot polymerization process for the preparation of stabilized thermoplastic resin or resins comprising heating a mixture comprised of a free radical initiator, a stable free radical agent, at least one polymerizable free radical reactive monomer compound, and optionally a solvent, to form a stabilized thermoplastic resin or resins with a high monomer to polymer conversion and a narrow polydispersity. The resulting stabilized thermoplastic resins may be the aforementioned intermediate polymer products which are useful as reactive emulsifiers or may be the aforementioned stabilized resin particles depending on the process procedures and conditions selected and as illustrated herein.

In embodiments, the present invention provides a polymerization process for the preparation of stabilized thermoplastic resin or resins particles for use as, for example, toners comprising forming a mixture comprised of at least one free radical reactive monomer, a colorant, a steric and/or electrostatic stabilizer compound containing a stable free radical reactive group, an optional emulsifier, and an optional polymeric resin wherein the optional resin is soluble or dispersible within said monomer, and a liquid vehicle; and heating the mixture to effect polymerization of said monomer, wherein there results stabilized core resin particles containing said colorant and wherein said stabilized core particles are stabilized by said stable free radical reactive stabilizer compound covalently bound thereto.

In embodiments, the processes of the present invention can be expanded to enable the formation of bimodal or multimodal thermoplastic resins by for example, adding to the aforementioned thermoplastic resin or resins a second mixture comprised of a free radical initiator, a stable free radical agent, and at least one polymerizable monomer compound as disclosed, for example, in US-A-5,412,047. The resulting mixture of thermoplastic resins possesses a modality of 2. Higher modalities, for example, of from 3 to about 20 can be conveniently achieved, if desired, by the subsequent addition of additional fresh mixtures of monomer, free radical initiator, and stable free radical agent prior to a final cooling and isolation step. The resulting resins in embodiments can be, for example, a bimodal mixture of a first homopolymer product resin comprising a diblock copolymer comprised of a first segment containing a block derived from a first monomer and a second block arising from the second monomer mixture, and a second product resin comprised of a homopolymer derived from substantially only the second monomer mixture.

There is additionally provided a method of imaging comprising: jetting with a liquid jetting means an ink jettable toner composition comprised of a liquid carrier vehicle and stabilized core particles comprised of resin, colorant, and a stabilizer component, in a predetermined pattern onto a receiving member to form an image; and fixing the image to a receiver by heating or irradiating the image and/or the receiver at from 40 to 150°C so that a durable and high quality image results therefrom.

In embodiments of the present invention, there are provided a toner composition comprising a liquid carrier vehicle, and marking particles comprised of a core resin or resins, optional a colorant and additives, and at least one stable free radical reactive polymeric stabilizer compound, which is substantially covalently attached to the resin particle surface or embedded in the resin particle core, that is a composition wherein the stable free radical reactive stabilizer compound is substantially chemically bound or covalently attached to the core resin, wherein for example, a hydrophobic end of the stabilizer compound is substantially embedded in the hydrophobic core resin particles. Also disclosed are compositions wherein the stable free radical reactive stabilizer compound is a block copolymer of the formula (A-B-)-SFR or (I-A-B)-SFR wherein A is a hydrophilic polymer or copolymer segment, B is a hydrophobic polymer or copolymer segment, I represents a free radical initiator reactant residue and wherein -SFR is a terminal and thermally labile latent stable free radical functional group covalently bonded to the B segment. Also disclosed are compositions and processes wherein the stable free radical block copolymer compound of the formula (A-B)-SFR or (I-A-B)-SFR when heated in the presence of core resin monomer affords a stabilized marking particle of the formula (A-B)_n-C where C represents the core polymer resin, (A-B) represents the stabilizer adduct bound directly to the core polymer resin via the hydrophobic block segment B, and wherein n is an integer from 1 to 10⁷ or alternatively up to 15 percent by weight of stabilizer compound to the total weight of the core resin and represents the number of polymeric stabilizer groups derived from the SFR reactive stabilizer compound which are bonded to the core polymer resin. From the foregoing discussion and the disclosure and working examples contained hereinafter it is readily apparent, and understood by one of ordinary skill in the art, that the free radical initiator reactant, fragment, or residue designated as I in the formula (I-A-B)-SFR is embodied in the alternative formula representation (A-B)-SFR.

There are also provided ink compositions comprising an aqueous liquid vehicle and marking particles with an average volume diameter of 0.3 to 10 microns comprised of at least one polymeric or copolymeric resin, a colorant, optional additives, and at least one polymeric or copolymeric stabilizer compound wherein the stabilizer compound is a block copolymer with a hydrophilic segment and a hydrophobic segment and wherein the hydrophobic segment is covalently attached to and embedded in the core polymer resin particles.

Embodiments of the present invention are directed to processes for the preparation of toner compositions comprising: heating a mixture of at least one free radical reactive pigment particle and a stabilizer compound of the aforementioned formula (I-A-B)-SFR containing a covalently bonded and thermally labile latent stable free radical reactive group to afford stabilized pigment particles, wherein the stabilized pigment particle has at least one stabilizer compound bonded directly thereto; dispersing and then heating the stabilized pigment particles and at least one free radical reactive monomer in a suspending liquid vehicle to form stabilized and pigmented resin particles wherein the stabilized pigment particles provide a loci and source of pseudoliving free radical species which polymerize the free radical reactive monomers thereon and stabilize the product against agglomeration or precipitation while in the suspending liquid vehicle.

The amount of stabilizer compound relative to the pigment used is selected to provide the desired level of stability to the resultant stabilizer-pigment adduct, for example, up to 10 to 15 weight percent of the stabilizer compound based on the weight of the pigment particles.

One class of monomers suitable for use in the present invention is C₃-C₆ monoethylenically unsaturated monocarboxylic acids, and known alkali metal and ammonium salts thereof. The C₃-C₆ monoethylenically unsaturated monocarboxylic acids include acrylic acid, methacrylic acid, crotonic acid, vinylacetic acid, and acryloxypropionic acid. Acrylic acid and methacrylic acid are the preferred monoethylenically unsaturated monocarboxylic acid monomers.

Another class of monomers suitable for the present invention is C₄-C₆ monoethylenically unsaturated dicarboxylic acids and the known alkali metal and ammonium salts thereof, and the anhydrides of the cis dicarboxylic acids. Suitable examples include maleic acid, maleic anhydride, itaconic acid, mesaconic acid, fumaric acid, and citraconic acid. Maleic anhydride and itaconic acid are preferred monoethylenically unsaturated dicarboxylic acid monomers.

The acid monomers selected may be in their acid forms or in the form of the alkali metal or ammonium salts of the acid. Suitable bases useful for neutralizing the monomer acids include sodium hydroxide, ammonium hydroxide and potassium hydroxide. The acid monomers may be neutralized to a level of from 0 to 50 percent and preferably from 0 to 20 percent. More preferably, the carboxylic acid monomers are used in the completely neutralized form, that is, for example, wherein the carboxylic acid functional groups (-CO₂H) are completely converted using stoichiometric or excess molar amounts of the appropriate base to corresponding carboxylate salts (-CO₂M) where M is an alkali metal or ammonium salt selected from the group of Li, Na, K, Rb, NR₄, where R is selected from the group of hydrogen, alkyl, alkenyl, alkylaryl, and aryl having from 0 to 20 carbon atoms.

Polymerizable monomers include monoethylenically unsaturated carboxylic acid-free monomers. Suitable monoethylenically unsaturated carboxylic acid-free monomers can be copolymerizable with the carboxylic monomers, for example alkyl esters of acrylic or methacrylic acids; hydroxyalkyl esters of acrylic or methacrylic acids; acrylamides; acrylonitriles; N-vinylpyrrolidone; styrene; hydroxylated styrenes; styrenesulfonic acid and salts thereof; vinylsulfonic acid and salts thereof; 2-acrylamido-2-methylpropane-sulfonic acid and salts thereof; and dially dialkyl quaternary ammonium salts.

Monomers, polymers and copolymers of the present invention can, in embodiments, be separated from one another or from the polymerization reaction mixture by, for example, solvent precipitation cooling, changing the pH of the reaction media, for example, from 7 to 4, and other well known conventional separation techniques.

The aforementioned monomers and comonomers can be used in polymerization reactions in amounts from 5 to 95 weight percent of the total weight of reactants.

Examples of suitable initiators selected for the processes of the present invention include any conventional free radical initiators which have a half-life of, for example, at least 1 second at the polymerization temperature. Preferably, the initiator will have a half life of from 10 second to 2 hours, more preferably from 10 seconds to 10 minutes at the reaction temperature. In another embodiment, a preferred heating profile is as follows: the initiator is added to the reaction mixture and then heated to 80 to 90 C from 5 minutes to 5 hours, and preferably from 30 minutes to 2 hours, to effect complete reaction of the initiator with the monomer(s), and then heating at 120 to 140 C for 1 to 20 hours to complete the polymerization of the monomer(s). These initiators include oxygen, hydrogen peroxide, certain alkyl hydroperoxides, dialkyl peroxides, peresters, percarbonates, peroxides, persulfates and azo initiators. The initiators are normally selected in amounts of from 0.05 percent to 33 percent based on the weight of total polymerizable monomer. A preferred range for preparing low glass transition temperature resin particles is from 0.5 to 20 percent by weight of the total polymerizable monomer. When the initiators are selected in amounts of 0.001 to 0.005 weight percent, weight average molecular weights in excess of 500,000 to 700,000 of the resulting polymeric particles can be obtained. In a preferred embodiment, an intermediate molecular weight stable free radical terminated stabilizer compound is first formed and then added to a second mixture containing additional monomer with the result that higher molecular weight polymers with narrow polydispersity may be achieved. Redox initiators may also be used, and may be added in amounts of 0.05 percent to 16 percent, based on the weight of total monomer. A preferred range is from 0.5 to 5 percent by weight of total monomer. It is preferred that the level of these initiators, if used, be minimized.

The stable free radical selected may be any known stable free radical agent which enables the objects of the present invention to be achieved. Examples of stable free radical compounds which are suitable for use in moderating the polymerization of the free radical reactive monomers include: 2,2,6,6-tetramethyl-1-piperidinyloxy free radical (TEMPO); 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinylxoy free radical; 2,2,5,5-tetramethyl-1-pyrrolidinlyoxy; 3-carboxy-2,2,5,5-tetramethyl-1pyrrolidinyloxy; and ditert-butyl nitroxide. The aforementioned stable free radicals and related derivatives, are satisfactory for the purpose of moderating the polymerization of a wide variety of different monomer types and comonomers, but are completely ineffective when used in homopolymerizations of acrylate monomers. The carbonyl containing stable free radical 4-oxo-2,2,6,6-tetramethyl-1-piperidinyloxy, (4-oxo-TEMPO) is effective for forming acrylate homopolymers and homopolymeric acrylate containing thermoplastic polymers. The stable free radical agents are selected in amounts of from 0.05 to about 35 percent based on the weight of the weight of the total polymerizable monomer. A preferred range is from 0.5 to 25 percent by weight of the total polymerizable monomer, and is used in approximately equivalent molar amounts, or preferrably, in slight molar excess amounts of the free radical initiator selected.

Stable free radical compounds are known, reference for example US-A-5,264,204 and 5,179,218, and "Synthetic Chemistry of Stable Nitroxides", by L. B. Volodarsky et al., CRC Press, 1993, ISBN:0-8493-4590-1.

The monomers of the present invention can be polymerized in a variety of polymerization reaction media. The reaction mixture may contain from 5 to 98 percent by weight, preferably from 25 to 85 percent by weight free radical reactive monomer with the balance comprised of other reactants, reagents, comonomers, colorants, and optional solvents or diluents.

The polymerization reactions of the present invention can be supplemented with a solvent or cosolvent to assist in ensuring that the reaction mixture remains a homogeneous single phase throughout the monomer conversion if desired. Any solvent or cosolvent may be selected providing that the solvent media is effective in permitting a solvent system which avoids precipitation or phase separation of the reactants or polymer products until after all polymerization reactions have been completed. The reaction solvent may be the same or different from the solvent selected as the liquid vehicle depending on the properties desired in the resulting formulation, for example, evaporation rates or volitility and monomer solubility. Exemplary solvents or cosolvents are polymer product compatible solvents or non-solvents which dissolve or readily disperse the polymer product, such as aliphatic alcohols, glycols, ethers and polyalkylene glycols, derivatives thereof, and mixtures thereof. Specific examples include ethylene glycol, glycerine, dipropylene glycol, tetrahydrofuran and mixtures thereof. When mixtures of water and water soluble or miscible organic liquids are selected as the reaction media, the water to cosolvent weight ratio typically ranges from 100:0 to 10:90, and preferably from 97:3 to 25:75.

Temperature of the polymerization may range from 75°C to 180°C, preferably from 110°C to 175°C and more preferably from 120°C to 140°C. At temperatures below 100°C, the reaction rate is slow and industrially impractical without the aid of an acid or base accelerating additive compound. At temperatures above about 180°C, conversion of the monomer into polymer decreases and uncertain and undesirable by-products are formed. Frequently, these by-products discolor the polymer mixture and may necessitate a purification step to remove them or they may be intractable.

Since solvent and cosolvent admixtures can be used as the reaction media, the elevated temperatures of the polymerization preferably select a polymerization reactor that is equipped to operate at elevated pressure.

The weight average molecular weights referred to herein are measured by gel permeation chromatography using, for example, a polyethylene oxide standards for water soluble polymers and polystyrene standards for organic soluble polymers unless specifically stated otherwise.

The present invention provides several specific advantages in embodiments as follows.

With the process of the present invention, polymer product polydispersities can be varied from between approximately 1.0 to approximately 2.0, or higher if desired, and preferably from 1.0 to less than 1.5 depending on the monomer/comonomer system selected and by varying the ratio of stable free radical agent to free radical initiator molar concentration. When the polymerization process conditions of the present invention are attempted with monomers without using the stable free radical (SFR) additive, considerably broader molecular weight resins are obtained for example, in excess of 2 to 3, and conversion rates and extent are lower than those of the present invention in embodiments.

An oxo substituted nitroxide stable free radical agent may be used in the situation where acrylate or acrylate ester homopolymerization products are desired, and which reactions can be performed in a variety of reaction media including bulk, solution, aqueous or organic emulsion, suspension, phase transfer, or reactive extrusion.

During the reaction of monomer or mixtures of monomers to form polymers, the reaction time may be varied over 1 to 60 hours, preferably between about 2 to 10 hours and optimally 3 to 7 hours. The optimal reaction time may vary depending upon the temperature, the volume and scale of the reaction, the quantity and type of polymerization initiator and stable free radical agent selected, and relative monomer reactivity.

The polymerization reaction temperature is retained relatively constant throughout the heating step by providing an adjustable external heat source. This temperature is from 60°C to 180°C, and preferably between 100°C and 160°C and optimally in embodiments 130°C to 160°C. Reactions performed above 200°C tend to result in a broadening of the polydispersity. A reaction volume may be selected for any size that enables simple adding, mixing, reacting, isolating, and formulating the product resins on an economic or convenient scale.

The free radical initiator can be any free radical polymerization initiator capable of initiating a free radical polymerization process of unsaturated monomers and includes peroxide initiators such as benzoyl peroxide, persulfate initiators such as potassium persulfate and azo initiators such as azobisisobutyronitrile. The initiator concentration employed is 0.001 to 20 weight percent of the total weight of monomer to be polymerized and is determined by the desired molecular weight of the resin. As the initiator concentration is decreased relative to the weight or molar equivalents of monomer used, the molecular weight or the thermoplastic resin product increases.

Known water soluble free radical initiators can be optionally employed in the processes of this invention and are those that are traditionally used in aqueous polymerization.

A preferred initiator is one which has a one-hour half-life at 60 to 95°C and a ten-hour half-life at 50 to 80°C. Other peroxides, such as peresters and peracids having somewhat higher one-hour half-life/temperature relationships, may also be used if they are accompanied by a promoter compound such as tertiary amine. Particularly preferred free radical initiators are azobisalkylnitrile and diaroyl peroxide compounds.

Water soluble monomer or monomers to be polymerized can be dissolved in water or aqueous mixtures of polar protic or aprotic organic solvents. The resultant aqueous solution usually contains a suitable water-soluble, free-radical generating initiator such as a peroxide or a persulfate, as defined above. The monomer or monomers are used in effective amounts relative to the free radical initiator, and stable free radical agent, as defined hereinafter.

Under the polymerization conditions of the present invention, the stable free radical agents function not as inhibitors but as moderators to harness the normally highly reactive and indiscriminate propagating intermediate free radical polymer chain species. The stable free radical agents are preferably soluble in the monomer phase, if more than a single phase is present initially, where predominantly all the polymerization of monomers occurs. Stable free radical agents which have limited monomer solubility are still useful, but may require a monomer miscible cosolvent or else these stable free radical compounds tend to result in less predictable polymerization processes. If the stable free radical agent separates out of the monomer phase to any great extent then the balance desired between the mole ratio of the stable free radical agent, free radical initiator, and propagating free radical polymer chain species may be upset.

The molar ratio of the stable free radical (SFR) agent to free radical initiator (INIT) residing in the monomer phase is from 0.5 to 5.0, and preferably in the range from 0.4 to 4.0. Although not desired to be limited by theory, in an embodiment, the molar ratio [SFR:INIT.] of stable free radical agent, for example, 4-oxo TEMPO, to free radical initiator, for example, AIBN, is 2.0 and is believed to be important for success of the process. If the [SFR:INIT.] is too high then the reaction rate is noticeably inhibited. If the [SFR: INIT.] is too low then the reaction product has undesired increased polydispersity. It should be noted that when acrylic acid or acrylate ester compounds are polymerized to polyacrylate derivatives without the stable free radical agent of the present process, the product polymers isolated have polydispersities of 2.0 and above. A preferred stable free radical is the aforementioned TEMPO, and oxo-TEMPO when acrylate homopolymers are desired, and with benzoyl peroxide as a preferred initiator.

In embodiments, the molar ratio of monomer content to stable free radical agent to free radical initiator is from 6.0:0.2:1.0 to 10,000:2.5:1.0 and preferably in the range of 125:2.0:1.0 to 7,000:1.3:1.0.

Processes of the present invention, in embodiments, provide for selective low, intermediate, and high monomer to polymer conversion rates, or degrees of polymerization, and preferably, for example, of 90 percent by weight or greater.

The low weight average molecular weight resin products having narrow polydispersity properties, as is also the situation with intermediate and high molecular weight products of the present invention, may be obtained without the use of a chain transfer agent.

Processes of the present invention, in embodiments provide for relatively high weight average molecular weights, from weight average molecular weights ranging in size of from 2,000 to 500,000 while delivering narrow polydispersity products with high conversion as defined and illustrated herein.

The polymerization reaction rate of the monomers may, in embodiments, be inhibited or accelerated and the reaction time influenced by the addition of a minor amount of a protic acid such as phosphoric, sulfuric, hydrochloric, camphor sulfonic acid and benzoic acid. The added acid may have a profound or very little effect on the polymerization rate, depending upon a variety of reaction variables and conditions. Excessive addition of inorganic and organic acid beyond equimolar amounts compared to the stable free radical agent causes the resin polydispersity to broaden. In embodiments, the protic acid source may be an acid functional group contained in either the stable free radical agent or in the free radical initiator compound.

By cooling the polymerization reaction to below 60 to 80°C, the stable free radical moderated polymerization process is effectively quenched or terminated. Each new or subsequent addition of mixtures containing monomer, stable free radical, and initiator, accompanied by heating above about 100° to 120° provides a new pseudoliving polymeric species having a narrow molecular weight distribution and each new polymer species continues to grow independently of the other polymer species already established thereby providing the capability of forming well defined, narrow polydispersity, bimodal and multimodal polymer mixtures which may or may not be water soluble.

Alternatively, block copolymer resins may also be prepared whereby after each desired block has been formed a new monomer or monomers is added, without the addition of more initiator or stable free radical agent, to form a new block wherein each block component is well defined in length and has a narrow molecular weight distribution and having properties depending on the repeated sequence and the monomers chosen for incorporation, for example, the second or subsequently added blocks may or may not be water soluble. Monomers added subsequent to the formation of the first formed thermoplastic resin may be water soluble or water insoluble. Judicious selection of the water solubility properties of added monomers and the resulting polymeric segment enables convenient synthetic routes to block and multiblock copolymers with narrow polydispersities that are useful, for example, as reactive emulsifiers or stabilizing surfactants, resin compatibilizers, viscosity modifies, and high efficiency emulsifiers.

The polymeric products of the present invention may be optionally crosslinked with, for example, known crosslinking, coupling, or curing agents such as divinyl benzene either in situ or in a separate post polymerization process step.

Additional optional known additives may be used in the polymerization reactions which do not interfere with the polymerization and particle forming reactions, for example, colorants, lubricants, release or transfer agents, surfactants, stabilizers, antifoams and antioxidants.

Ink and dry toner formulation resins possessing a discrete mixture of monomodal resins, that is a well defined multimodal molecular weight distribution, may in embodiments thereof provide several advantages, particularly for electrophotographic and ink jettable type fusible toner compositions such as: melt rheology properties including improved flow and elasticity; and improved performance properties such as triboelectrification charging of particles, admix rates, improved ink jetting performance as measured by latency and recoverability, and shelf life stabilities.

Referring to the Figures, toner compositions can be prepared by a number of known methods, such as admixing and heating the aforementioned reactive emulsifier compounds of the formula (I-A-B)-SFR with resin particles 1 having free radical reactive double bonds 5 on the surface thereof and optional colorants, reference Figure 1. Free radical reactive double bonds include for example, double bonds which bear substituents selected from the group, hydrogen, alkyl, aryl, alkylaryl, carbonyl, olefinic and halides. The resulting stabilized resin particles 2 wherein the aforementioned double bonds 5, have reacted with the reactive emulsifier compounds, are converted to saturated bonds 6 by the free radical addition of

reactive emulsifier fragments

7 and 8. The particles 2 can be further surface modified by heating the particles to above 100 to 120°C, when the substituents on the saturated bond bearing the stable free radical (SFR) group are selected from the group, aryl, alkylaryl, carbonyl, olefinic and halides, preferably in a non-dissolving liquid suspension, with an additional free radical reactive monomer or monomers, sequentially or as mixtures, to afford stabilized resin particles 3 with supplemental appendages 9 derived, for example, from monomers C and D as illustrated in Figures 1 and 2. When the additional monomers are added sequentially, (C)-(D) block copolymer appendages result. When the additional monomers are added as a mixture, random copolymers of the form (C-D) result and which randomness is governed by the relative reactivity ratios of the respective monomers. Alternatively, in embodiments, the reactive emulsifiers (I-A-B)-SFR may be reacted directly with free radical reactive monomer or monomers, optionally in the presence of a colorant 10, reference Figure 2, and optionally with a stabilized colorant adduct or particle of the present invention, as illustrated in Figure 3 wherein 10 is the colorant or pigment such as carbon black, and heat refers, in embodiments, to 120° to 160°C. The resulting stabilized pigment particles and stabilized resin particles can be water or oil dispersible depending upon the selection and constitution of the reactive stabilizer compounds affixed to the particles.

Furthermore, in embodiments there are provided processes for preparing stabilized pigment particles by heating suitably reactive pigment particles with a stabilizing quantity of the reactive emulsifier. The resulting stabilized pigment particles may be further admixed and heated with free radical reactive monomer and optional resin to polymerize the monomer onto the pigment particle which further compatibilizes and dispenses the pigment particles with incipient resin and resin particles, and thereby leads to colorized resin particles with highly uniform pigment particle dispersions and color quality properties, reference Figure 3.

In other embodiments, stabilized resin and pigment particles with stable free radical (SFR) surface groups may be heated in the presence of a protic acid in the absence of monomer, or alternatively by photolysis, to effectively cleave the -SFR surface groups and thereby provide stabilized resin and pigment particles which are substantially free of surface -SFR groups. The aforementioned acidic treatment affords a simple means for introducing enhanced thermal and chemical stability to the stabilized resin and pigment particles by removing the thermally and photochemically labile latent free radical functionality from the particle surface.

Ink compositions can be prepared by a number of known methods, such as admixing and heating polymer suspensions obtained with the processes of the present invention such as water soluble styrene sulfonates with pigment particles such as magnetite, carbon black, surface treated carbon blacks such as ACETYLENE BLACK® from Chevron Oil and CONDUTEX SC, and mixtures thereof, and cyan, yellow, magenta, green, brown, red, or mixtures thereof in amounts of from 0.5 to 15 weight percent of the total monomer and resin used in an attritor device, such as the 01 Attritor available from Union Process and removing the formed ink composition from the device. After cooling, the ink composition is optionally subjected to filtration, for example, through a 0.8 micron filter for the purpose of achieving pigment dispersions with a volume median diameter of less than 0.10 microns, and preferably of from 0.03 to 0.08 micron, which diameters are determined by a HORIBA particle sizer.

Subsequent to cooling, the toner composition, if desired but not necessary, is subjected to grinding utilizing, for example, a Sturtevant micronizer for the purpose of achieving toner particles with a volume median diameter of less than 25 microns, and preferably of from 6 to 12 microns, which diameters are determined by a Coulter Counter. The toner compositions can optionally be classified if desired utilizing, for example, a Donaldson Model B classifier for the purpose of removing toner fines, that is toner particles less than about 4 microns volume median diameter, for use in, for example, dry toner marking applications.

Illustrative examples of suitable toner and ink resins and co-resins selected for the toner and ink developer compositions of the present invention include polyamides, styrene acrylates, styrene methacrylates, styrene butadienes, vinyl resins, including homopolymers and copolymers of two or more known vinyl monomers.

In concentrated liquid toner and ink compositions, the marking particles are present in a sufficient but effective amount, for example, from 10 to 90 weight percent. Thus, for example, when 1 percent by weight of the charge enhancing additive is present, and 10 percent by weight of pigment or colorant, such as carbon black, is contained therein, about 89 percent by weight of resin is selected. Also, the charge enhancing additive may be optionally coated on the pigment or pigmented resin particle. When used as a coating, the charge enhancing additive is present in an amount of from 0.1 weight percent to 5 weight percent, and preferably from 0.3 weight percent to 1 weight percent.

There can also be blended with the toner compositions of the present invention external additive particles including flow aid additives, which additives are usually present on the surface thereof. Examples of these additives include colloidal silicas, such as AEROSIL®, metal salts and metal salts of fatty acids inclusive of zinc stearate, aluminum oxides, cerium oxides, and mixtures thereof, which additives are generally present in an amount of from 0.1 percent by weight to 5 percent by weight, and preferably in an amount of from about 0.1 percent by weight to 1 percent by weight.

With further respect to the present invention, colloidal silicas, such as AEROSIL®, can be surface treated with the charge additives in an amount of from 1 to 30 weight percent and preferably 10 weight percent followed by the addition thereof to the toner in an amount of from 0.1 to 10 and preferably 0.1 to 1 weight percent.

Also, there can be included in the toner compositions low molecular weight waxes, such as polypropylenes and polyethylenes commercially available from Allied Chemical and Petrolite Corporation. Many of the polyethylene and polypropylene compositions useful in the present invention are illustrated in GB-A-1,442,835.

The low molecular weight wax materials are optionally present in the toner composition or the polymer resin beads of the present invention in various amounts, however, generally these waxes are present in the toner composition in an amount of from 1 percent by weight to 15 percent by weight, and preferably in an amount of from 2 percent by weight to 10 percent by weight and may, in embodiments, function as fuser roll release agents.

In embodiments of the present invention there are provided ink jettable toner compositions and imaging processes thereof wherein the ink and resulting developed images have a latency of 5 seconds to 2,000 seconds, and a recoverability of 50 seconds to 2,000 seconds, where latency is defined as the time that a printhead can maintain transit times (between the printhead and the paper) of below 100 microseconds and where recoverability is defined as the time that a printhead can regain transit times below 100 microseconds. The resulting developed and fused images, in embodiments, possess excellent mid frequency line edge noise known as MFLEN, also referred to as line raggedness, of 1 to 10, and preferably from 1 to 3.

For the formulation of dry developer compositions, there are mixed with the toner particles carrier components, particularly those that are capable of triboelectrically assuming an opposite polarity to that of the toner composition. Accordingly, the carrier particles are selected to be of a negative polarity enabling the toner particles, which are positively charged, to adhere to and surround the carrier particles. Examples of carrier particles include iron powder, steel and ferrites. The selected carrier particles can be used with or without a coating, the coating generally containing terpolymers of styrene, methylmethacrylate, and a silane. Coating weights can vary as indicated herein; generally, however, from 0.3 to 2, and preferably from 0.5 to 1.5 weight percent coating weight is selected.

The toner and ink compositions of the present invention can be prepared by a number of known methods as indicated herein including direct isolation of the aforementioned in situ particles by known means, extrusion melt blending the stabilized toner resin particles with conventional colorant compounds, optionally the stabilized pigment particles or colorants, and optionally a charge enhancing additive, followed by mechanical attrition. Other methods include those well known in the art such as spray drying, melt dispersion, emulsion aggregation, and extrusion processing.

The toner and developer compositions may be selected for use in electrostatographic imaging apparatuses containing therein conventional photoreceptors providing that they are capable of being charged positively or negatively.

The toner compositions may be optionally jetted and classified subsequent to preparation to, although not believed to be necessary for the aforementioned reasons, enable toner particles with a preferred average diameter of from 5 to 25 microns, and more preferably from 8 to 12 microns. Also, the toner compositions preferably possess a triboelectric charge of from 0.1 to 2 femtocoulombs per micron as determined by the known charge spectrograph.

Also, the toner compositions prepared from resins of the present invention possess desirable narrow charge distributions, optimal charging triboelectric values, preferably of from 10 to 40, and more preferably from 10 to 35 microcoulombs per gram as determined by the known Faraday Cage methods with from 0.1 to 5 weight percent in one embodiment of the charge enhancing additive; and rapid admix charging times as determined in the charge spectrograph of less than 15 seconds, and more preferably in some embodiments from 1 to 14 seconds.

The following Examples are being supplied to further define various species of the present invention, it being noted that these Examples are intended to illustrate and not limit the scope of the present invention. Parts and percentages are by weight unless otherwise indicated.

EXAMPLE I Preparation of Polystyrene Sulfonates/Polystyrene Block Copolymer Containing Stable Free Radical Reactive Group.

To an aqueous solution of ethylene glycol (97.5%) was added sodium styrenesulfonate monomer (100 g, 0.486 mol), TEMPO (19.6 g, 0.126 mol), and sodium bisulfate (8.1 g). This mixture was heated in an oil bath under argon, at 50°C until the solids dissolved, and then potassium persulphate (16.2 g, 0.6 mol) was added. The solution was maintained at this temperature for 2.5 hours, and then heated to reflux (120°C) for 4.5 hours. After the solution was cooled to about 80°C, it was then added to a solution of acetone/methanol (1.4 L, 7:3), resulting in a paste. The supernatent was decanted off and 1L of acetone added. This mixture was stirred for 10 minutes and the resulting precipitate was filtered, washed with acetone, hexane, and then dried to give 83.8 g of polymer. Molecular weight of the poly(styrene sulfonate)-TEMPO intermediate polymer as determined on a Shimadzu gel permeation chromatograph (aqueous sodium nitrate as eluant) was M_w = 8,722 with a polydispersity of 1.35.

To ethylene glycol (40 g) was added 10 g of the above mentioned sodium poly(styrene sulfonate), and styrene monomer (10 g). This solution was heated to 130°C and maintained at that temperature for 6 hours. The solution was cooled and added to acetone (350 mL). The resulting precipitate was filtered, washed twice with acetone and twice with hexane. After drying, 13 g of poly(sodium styrenesulfonate-b-styrene)-TEMPO copolymer with a M_w = 11,250, and P.D. = 1.19 was obtained for a styrene monomer to copolymer weight conversion of about 65 percent.

EXAMPLE II Preparation of Colored Resin Particle Emulsions.

To 2 g of the block copolymer prepared in Example I was added water (100 mL), styrene monomer (18 g) and a blue oil soluble dye (5 g, BASF LURAFIX BLUE) in a PARR reactor. This two phase system was vigorously stirred and heated to 130°C. The mixture was maintained at 120°C to 130°C for 5 hours, cooled and then filtered through a 0.7 micron filter to provide a filtrate containing a blue colored resin particle emulsion useful as a liquid ink jettable toner.

EXAMPLE III Evaluation of Ink Jettable Toners.

The filtered emulsion of Example II was evaluated as a working ink in a Hewlett-Packard thermal ink jet (TIJ) printer Model HP500C from Hewlett-Packard Corp. Images were jetted and then fused on a refuser at 150°C. The optical density (O.D.), water fastness, and wet smear of the resultant images were measured using a densitometer both before (no heat) and after fusing (heat 150°C). The results are shown in the accompanying table.

Jetted Toner Evaluation	O.D. (No Heat)	O.D. (Heat 150°C)
Image direct from HP printer	0.54	0.54
Waterfastness-Image exposed to H₂O	0.25	0.46
Image wet smear	0.34	0.52

The optical density results indicated that after heating and fusing the images to the receiver, the fused images are highly resistant to water and wet smear and are comparable to the water fastness and wet smear properties of conventional fused dry toner xerographic images.

EXAMPLE IV

Preparation of Stabilized Carbon Black Suspensions. The poly(styrene sulfonate)-TEMPO first formed intermediate polymer of Example I, (M_w 8,722, polydispersity 1.35) 4 g, was added to an attritor containing 2 kg of 440C stainless steel shot and 220 g of 97% aqueous ethylene glycol with stirring. The attritor was heated to 100°C with an oil heated jacketed attritor. Carbon black (20 g, RAVEN 5750 from Columbia Chemicals) was added over a 1 minute period and heating continued to 135°C. Attrition was continued for 7 hours, then cooled to 25°C and resultant stabilized carbon black pigment paste was suctioned off from the shot. Residue from the shot was recovered by washing the shot twice with 250 g portions of H₂O. The combined aqueous dispersions were centrifuged for 40 minutes at 4,000 RPM. The supernatent was discarded. The sediment was redispersed in H₂O (350 g), then sonicated for 20 minutes. The dispersion was centrifuged a second time (20 min at 4,000 RPM) and the supernatent was filtered through a 0.7 micron filter, then rinsed with about 5 ml of H₂0 to complete the transfer. The filtrate afforded 354 g with a solids content of 18.1 g comprised of stabilized carbon black particles suspended in water. This passivated and stabilized carbon black particle dispersion in H₂O was used as a stock suspension for preparing ink formulations.

Aqueous Ink Jet Toner Formulation. To 75 g of the above stock suspension was added 20 g ethylene glycol, 3 g of isopropyl alcohol and 2 g H₂O. This ink formulation afforded a final carbon black loading of 4.5% by weight. This ink formulation was tested on an ink jet print head simulator, whereby the jetted drops were observed in flight with opto-electronic instrumentation, and relative drop sizes, velocities, and other drop characteristics were measured and recorded. The measured latency was greater than 1,000 seconds using a 300 s.p.i. simulated printhead configuration.

EXAMPLE V

Preparation of High Weight Average Molecular Weight Poly(styrenesulfonate)-TEMPO Terminated Stabilizer Compound (PSS-T). To a 100 mL round bottom flask was added styrene sulfonate sodium salt monomer (10 g, 0.0486 mole), TEMPO stable free radical (1.52 g, 0.00972 mole), NaHSO₃ free radical initiator ( 0.65 g ) and benzoic acid as a rate accelerant (300 mg). To this was added 31 g of ethylene glycol and 8 g of water. This solution was heated to 70 °C for 1 hour and then heated to reflux for 1.5 hours. Next 6 mL (about 10% by volume) of the aforementioned reaction solution containing primarily poly(styrenesulfonate)-TEMPO terminated reactive stabilizer compound of intermediate molecular weight was added to a second solution of styrene sulfonate sodium salt monomer (100 g, 0.486 mole) solution contained in an ethylene glycol/water (320 g/80 g) mixture. This mixture was heated at reflux for 2.5 hours and then poured into a mixture of methanol/acetone to give a polymer product after drying of 88 g in an 87% yield. The PSS-T polymer product was analyzed and found to have the following molecular weight properties: M_w= 216,690; M_n=162,259; and polydispersity (M_w/M_n) of 1.34.

EXAMPLE VI

When Example V is repeated with the exception that only 1 mL (less than 2% by volume) of the first formed reaction mixture containing the intermediate molecular weight TEMPO terminated stabilizer compound is added to the second solution of monomer wherein a final PSS-T polymer product with an estimated weight average molecular weight in excess of about 500,000 and a polydispersity of less than 1.5, that is about 1.4 is obtained.

EXAMPLE VII

Example V was repeated with the exception that only 0.1 mL (less than 0.2% by volume) of the first formed reaction mixture containing the intermediate molecular weight TEMPO terminated stabilizer compound was added to the second solution of monomer with the result that the final PSS-T polymer product had a weight average molecular weight of about 700,000 and a polydispersity in excess of 2.0.

EXAMPLE VIII

Preparation of Uncolored Resin Particle Emulsions. To 1.0 g of a reactive block copolymer poly (styrenesulfonate-b-styrene)-TEMPO was added water (100mL), styrene (12.1g) and dodecylbenzylsulfonic acid (0.30g) in a PARR reactor. The resultant two phase system was emulsified with a high shear mixer for 1 minute. The PARR reaction vessel was purged with nitrogen, sealed, and then heated to 125°C over 45 minutes. This temperature was maintained for 6 hours with rapid stirring. The reactor was cooled and the emulsion was discharged. The yield for the reaction was 59 weight percent solids based on the weight of the reactants. The particle size as determined by SEM was 10 to 100 nm. The emulsion at room temperature showed no settling, phase separation, or agglomeration over an extended period of time.

EXAMPLE IX

Magnetic Toner Preparation and Evaluation. The amphipatic diblock polymer resin (74 weight percent of the total mixture) obtained by the stable free radical polymerization processes of Example I may be melt extruded with 10 weight percent of REGAL 330® carbon black and 16 weight percent of MAPICO BLACK^® magnetite at 120°C, and the extrudate pulverized in a Waring blender and jetted to 8 micron number average sized particles. A positively charging magnetic toner may be prepared by surface treating the jetted toner (2 grams) with 0.12 gram of a 1:1 weight ratio of AEROSIL R972® (Degussa) and TP-302 a naphthalene sulfonate and quaternary ammonium salt (Nachem/Hodogaya Sl) charge control agent.

Developer compositions may then be prepared by admixing 3.34 parts by weight of the aforementioned toner composition with 96.66 parts by weight of a carrier comprised of a steel core with a polymer mixture thereover containing 70 percent by weight of KYNAR®, a polyvinylidene fluoride, and 30 percent by weight of polymethyl methacrylate; the coating weight being about 0.9 percent.

Claims

A process for the preparation of stabilized core resin particles comprising: forming a mixture comprised of at least one free radical reactive monomer, a polymeric stabilizer compound containing a covalently bonded stable free radical reactive group, a liquid vehicle and optionally a colorant; and heating the mixture from 75 to 200°C to effect polymerization of said monomer.
A process in accordance with claim 1 wherein the monomer is a hydrophobic monomer selected from the group consisting of monovinyl aromatic compounds and derivatives thereof, dienes and derivatives thereof, and acrylates and derivatives thereof.
A process in accordance with claim 1 wherein the polymeric stabilizer compound of the formula (A-B)-SFR is selected from the group consisting of poly(styrenesulfonate-b-styrene)-SFR, poly(acrylic acid-b-styrene)-SFR, and poly(alkyl acrylate-b-styrene)-SFR wherein -SFR is a covalently bonded and thermally labile stable free radical functional group.
A process in accordance with claim 1 further comprising adding to the mixture prior to heating a thermoplastic resin selected from the group consisting of polystyrenes, polyacrylates, polymethacrylates, polydienes, mixtures thereof, and copolymers thereof, and wherein the resin is soluble or dispersible in the monomer component.
A resin composition comprising a liquid carrier vehicle, and stabilized core resin particles comprising core resin, optional colorant and additives, and at least one polymeric stabilizer compound derivable from a stable free radical containing compound.
A composition in accordance with claim 5 wherein the polymeric stabilizer compound is substantially chemically bound or covalently attached to the core resin, and wherein a hydrophobic end of the stabilizer compound is substantially embedded in the core resin particles and a hydrophilic end of the stabilizer compound is substantially distal to the particle surface.
A composition in accordance with claim 5 wherein the polymeric stabilizer compound is a block copolymer of the formula (A-B-)-SFR wherein A is a hydrophilic polymer or copolymer segment, B is a hydrophobic polymer or copolymer segment, and wherein the -SFR represents a thermally labile stable free radical functional group covalently and terminally bonded thereto.
An ink composition comprising an aqueous liquid vehicle and marking particles with an average volume diameter of 0.1 to 10 microns comprised of at least one polymeric or copolymeric resin, a colorant, optional additives, and at least one stabilizer compound wherein the stabilizer compound is a block copolymer with a hydrophilic segment and a hydrophobic segment wherein the hydrophobic segment is covalently attached to and embedded in the core polymer resin particle and wherein the hydrophilic segment is substantially extended into the aqueous liquid vehicle.
A process for the preparation of toner compositions comprising heating a mixture of core polymeric resin particles containing a colorant, at least one polymeric stabilizer compound containing a covalently bonded and thermally labile stable free radical reactive group, and optionally a liquid vehicle to afford stabilized toner particles.
A process for the preparation of toner compositions comprising: heating a mixture of at least one free radical reactive pigment particle and a reactive stabilizer compound containing a covalently bonded and thermally labile stable free radical reactive group to afford sterically stabilized, and optionally electrostatically stabilized, passivated pigment particles wherein the stabilized pigment particles have at least one stabilizer compound bonded directly thereto; dispersing and then heating the stabilized passivated pigment particles and at least one free radical reactive monomer in a suspending liquid vehicle to form stabilized resin particles containing the stabilized pigment particles, and wherein the stabilized pigment particles provide a locus and source of pseudoliving free radical species which polymerize the free radical reactive monomers thereto.
A process for the preparation of stabilized core resin particles comprising: admixing resin particles having free radical reactive double bonds on the surface thereof with polymeric stabilizer compound containing a covalently bonded stable free radical reactive group, and optionally a colorant; and heating the mixture from 75 to 200°C to effect reaction.